In order to achieve the desired therapeutic effect of a bioactive agent, an appropriate amount of the administered drug should be delivered into the target cells in a body. For this, a submicronic particulate drug delivery system using biodegradable polymers is being studied and as its typical example, nanoparticle system and polymeric micelle system have been reported as a technology of reducing side effects and enhancing efficiencies by modifying in vivo distribution of an intravenously-injected drug. Such drug delivery system can adjust the release of a drug into the target organs, tissues, or cells, and has been reported to have excellent biocompatibility and enhance the solubility of an insoluble drug and the bioavailability of a drug.
However, the polymer usually used for the preparation of polymeric nanoparticles or polymeric micelles is currently a diblock amphiphilic block copolymer (mPEG-PLA) comprised of a hydrophilic block such as monomethoxypolyethyleneglycol (mPEG) and a hydrophobic block such as polylactic acid (PLA), and since this polymer tends to be hydrolyzed in an aqueous solution, its final product is provided in the form of a lyophilized powder or cake.
Thus, in using as a drug carrier the above polymer which is stored in a solid state after lyophilization, it is inconvenient because it has to be dissolved again in a distilled water right before the use thereof. Moreover, the lyophilization increases the manufacturing costs and it causes a stability issue because there are possibilities of concentration change and microbe contamination during the reconstitution thereof.
Accordingly, if a final product can be provided in an aqueous solution state by enhancing the stability of a polymeric drug carrier in the aqueous solution state, it is expected that its manufacturing time will be shortened and it will be readily applicable as a drug carrier.